THEMIS: The Thermal Emission Imaging System

By looking at the visible and infrared parts of the spectrum, THEMIS is determining the distribution of minerals on the surface of Mars and helping scientists understand how the mineralogy of the planet relates to the landforms.

A word from THEMIS' lead scientist

How THEMIS Works in the Infrared

During the martian day, the sun heats the surface. Surface minerals radiate this heat back to space in characteristic ways that can be identified and mapped by the instrument. At night, since it maps heat, the imager searches for active thermal spots.

In the infrared spectrum, the instrument uses 9 spectral bands to help detect minerals within the martian terrain. These spectral bands, similar to ranges of colors, can obtain the signatures (spectral "fingerprints") of particular types of geological materials. Minerals, such as carbonates, silicates, hydroxides, sulfates, hydrothermal silica, oxides and phosphates, all show up as different colors in the infrared spectrum. This multi-spectral method allows researchers to detect in particular the presence of minerals that form in water and to understand those minerals in their proper geological context. THEMIS' infrared capabilities have significantly improved the data from TES, a similar instrument on Mars Global Surveyor.

The instrument's multi-spectral approach also provides data on localized deposits associated with hydrothermal and subsurface water and enables 100-meter (328-feet) images of martian terrain to be captured in each pixel, or single point, of every image.

ASTER, an Earth orbiting instrument on the Terra spacecraft, has used a similar approach to map the distribution of minerals here on Earth. Variations in the thermal infrared "color" in the right-hand image are due to differences in the kinds of minerals that make up rocks and soil. In the visible part of the spectrum that our eyes can see (left-hand image), it would not be apparent what minerals are present.

How THEMIS Works in the Visible

Using visible imaging in five spectral bands, the experiment also takes 18-meter-resolution (59-foot) images to determine the geological record of past liquid environments on Mars. More than 15,000 images-- each 20X20 kilometers (12X12 miles)-- have been acquired for martian surface studies. These more detailed data were used in conjunction with mineral maps to identify potential landing sites for the 2003 Mars Exploration Rover mission and new images will be used for future Mars missions.

The part of the imaging system that takes pictures in visible light is able to show objects about as big as a semi-truck. This resolution helps fill in the gap between large-scale geological images from the Viking orbiters in the 1970s and the very high-resolution images from the currently orbiting Mars Global Surveyor.

THEMIS Specs

For more information, visit the THEMIS instrument site at Arizona State University